Question

how can i write this code in java?

public class ComponentsManager 
    {
        private List<IComponent> list = new ArrayList<IComponent>();

        public <U extends IComponent> U GetComponent() {

            for (IComponent component : list) {

                if(component instanceof U)
                {
                    return component;
                }
            }
        }
}

but i cant perform instanceof on generic types. how should i do it?
thanks.

Answer 1

Basically you can’t do that due to type erasure. The normal workaround is to pass a Class object as a parameter; e.g.

    public <U extends IComponent> U GetComponent(Class<U> clazz) {
        for (IComponent component : list) {
            if (clazz.isInstance(component)) {
                return clazz.cast(component);
            }
        }
    }

You could also use if (clazz.equals(component.getClass())) { ... but that does an exact type match … which is not what the instanceof operator does. The instanceof operator and the Class.instanceOf method both test to see if the value’s type is assignment compatible.